How would I produce a chart of the pressure for a given potential temperature. When I do pressure (isentropic) for an isentropic surface (310K for example), I get a value of 1228299.4 at LCH. A skew-t for the exact time tells me the 600mb level has a theta of 310K. Am I doing something wrong? I am misinterpreting the data? What unit is the 1228299.4